###### tags: `CPE-數學計算`
# *B2-Sequence*
## 題目：

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <set>
using namespace std;

int main(void)
{
   int case_number;
   //int sum=0;
       vector<int> number_list;
       set<int> sum_record;
       int temp;
       int twice=0;
       cin>>case_number;
       //Get All Number
       for (int i=0;i<case_number;i++){
           cin>>temp;
           number_list.push_back(temp);
       }
       //Sum
       for (int i=0;i<number_list.size();i++){
           for (int j=i;j<number_list.size()-i;j++){
               if(sum_record.count(number_list[i]+number_list[j])==true){
                   twice++;
               }
               sum_record.insert(number_list[i]+number_list[j]);
           }
       }
       //cout<<twice<<endl;
       if (twice == 0){
           cout<<"Case #"<< number<<":"<<" It is a B2-Sequence."<<endl;
       }
       else{
           cout<<"Case #"<< number<<":"<<" It is not a B2-Sequence."<<endl;
       }
   
   return 0;
}